Process for changing the solubility of cellulose acetate



Patented Mar. 19, 1935 I 1,994,599

UNITED -STATES PATsr orricE PROCESS FOR CHANGING THE SOLUBILITY F CELLULOSE ACETATE Charles s. Webberand Cyril J. Stand, Rochester, N. Y., assignors to Eastman Kodak Company, Rochester, N. Y., a corporation of New York No Drawing. Application September 26, 1929,

Serial No. 395,453

9 Claims. (01. 260-102) This invention relates to a process for the necessary that the gaseous medium be present hydrolysis of cellulose esters and particularly to in thehydrolyzing bath throughout the period the hydrolysis of chloroform soluble cellulose of hydrolysis although in some instances itwill acetate to acetone solubility. be evident that such a thorough conditioningof There are a great number of known methods the'cellulose acetate may not be required. 5 for the preparation of cellulose acetate to the The gaseous mediums which 'we-have found fully acetylated ester, the triacetate, and there suitable for this purpose are the unsaturated are equally as many processes for the hydrolysis hydro-carbons of the ethylene series, particularly of this triacetate ofcellulose which is generally ethylene, and also sulfur dioxide. These gases 10 designated as chloroform soluble cellulose aceare suitable for use not only with the cellulose l tate to a solubility in acetone or other solvent. acetate, which at the present time is the organic This hydrolysis is generally carried out in a soluester of cellulose which is of the greatest importion of acetic acid as such a solution results when tance from the commercial standpoint, but likecellulose triacetate is synthesized by the acetylawise are useful for the hydrolysis'of other organic tion of cellulose in'an acetic anhydride-acetic esters of cellulose, such for examplaas cellulose 15 acid bath containing a suitable catalyst. Water formates, propionates, butyrates and like acyl is generallyadded to this bath, to stop further esters of cellulose. V acetylation of the cellulose, together with a hy- These gases may be added'to the hydrolyzing drolytic catalyst, such as strong mineral acids, bath in any one of a number of ways some. of

acid salts and the like{ the resulting solution which will readily suggest themselves to those 20 being maintained at atemperature of approxiskilled in this art. For example, we have found mately 50 C. with the production of the acetone it, in many instances, advantageous to dissolve soluble variety of the cellulose acetate in a matthe gas in a suitable liquid such as glacial acetic ter of 18 to 48 hours. The cellulose acetate is acid" and then add the charged acid. to the separated from the by-products of the reaction hydrolyzing bath." Other compatible solvents 25 by precipitation thereof in water. which will dissolvethe gas and which are like- Cellulose acetate, when thus prepared, whil wiseamenable to thehydrolyz'ing bath may be suitable for many purposes in which" the color of used as a carrier of the gas. Or the gas may, if the cellulose acetate is not of prime importance, desired, be bubbled into the hydrolyzing bath by 0 is not, however, the best type of cellulose acetate simply immersing therein a suitable tubing 0- for use in the photographic and rayon arts or, through which the gas is injected into and for that matter, in the lacquer industry where throughout the mass. Another method for its the lacquer is to be used clear. This is due to introduction may be the generation of the gas the fact that the film obtained fromsuch a celluwithin the hydrolyzing mixture either by chemilose acetate is generally of a slightlyyellow orj cal or electrolytic action. The sulfur dioxide, 35 brown color which is objectionable particularly for example; may be generated in situ by the for thick films. To utilize thisproduct it is often action of the acetic acid solution on sulfites and necessary to submit the hydrolyzed cellulose bisulfites, the water soluble. bisulfitessuch as esters to a final bleaching operation. sodium bisulfites being preferable. The use of 40 An object of the present invention isto provide such salts, however, are apt to inhibit the 40 a process for the hydrolysis of cellulose esters. hydrolytic catalyst and it should be borne inmind Another object is to conduct the hydrolysis of that a correspondingly increased amount therecellulose esters in theipresence of a gaseous meof should, the'refore,-be added to fully hydrolyze dium whereby the ester is simultaneously hytheester. WhileEthdaddition of sulfurous acid drolyzed and bleached. A further object is to accomplishes much the same purpose as sulfur eifect a reduction in the viscosity of the cellulose dioxide its use is much more limited than the acetate during its hydrolysis. Other objects will direct absorption of sulfur dioxide by the soluhereinafter appear. tion since the solvent water in the sulfurous acid We have found that the introduction of certain will markedly change the rate of hydrolysis of gases into the cellulose acetate solution before, the cellulose ester. 50 during or after hydrolysis produces a whiter While the gases named are generally added to product which, when dissolved in a suitable the hydrolyzing bath at or about room temperasolvent liquid, has a greater fluidity than the ture and atmospheric pressure the addition may cellulose acetates or esters prepared by the usual be made at higher temperature and pressure if so processes. To produce the optimum results, it is desired in order that a greater concentration of 55 ness of the cellulose ester when it is precipitated after hydrolysis and particularly so if the precipitating bath be heated to a temperature which. rapidly releases the dissolved gas from solution.

This advantageous result is likewise evident when carrying out the operations at room temperature and atmospheric pressure. The flufiing ofthe cellulose acetate by this action has many advantages as it renders the subsequent washing and later drying and re-dissolving of the ester more readily and quickly carried out.

The concentration of the gaseous medium in the bath will vary considerably with the type of the. cellulose ester it is desired to obtain. If a cellulose ester of maximum fluidity and whitenessiis sought a greater concentration of the gaseous medium should be used, although for most purposes the concentration as described in the following examples is satisfactory.

We shall now give several examples for carrying out our invention but it shall be distinctly understood that we are not limited by the propor-. tionsor other details therein given except as they are indicated in the appended claims.

Example ie-Into 360 parts of cellulose acetate solution resulting from the acetylation of cellulose as'prepared, for instance, by the process-describedin U. S. Pa.tent.1,683,34'7' of Le, B.'.Gray. and C. J. Staud in which the excess of'acetic anhydride has been destroyed with therequisite quantity of water and to which an excess of 20. partssof: water'have been addedivith'two parts of concentratedhydrochloric acid (sp; g. 1.19) sulfur:

dioxide is bubbled as rapidly as it can be'absorbed with. thorough stirring for a periodof 15 minutes. The gas is then shut off and 15' minutesafter the hydrolysis has been under way. for aperiodof' approximately 10 hours, the whole solution is held'at40l to C: for 6 hours and finally for 16 hours at room temperature. Sulfur dioxide is'again passed into the solution for 30 minutes;

' just prior to the precipitation in water at a temperature of 40. to C. Since a large volumeofgas is dissolved in the solution. on p'ouringyin a fine stream into warm water a flufiy product is obtained'ywhich is readily Washed free of acid. On comparing the acetone solution of this productwith that of a product from a check run from;

the same preparation, but without. the additionof sulfur dioxide; it'was found. that the, gaseous treatment gave a muchiwhiter solution with approximately the viscosity'of' thecellulose acetate into whichthe sulfur dioxide had been passed. Example 2.-600 parts of; cellulose tiiacetate were prepared as describedinthe above example,

to which 26 parts. of water dissolvedin 40 partsoi glacial acetic acid may be added. Ethylene is then introduced through a suitable glass tube, drawn out to a small tip, from a-tank of the com-. pressed gas. During 30 minutes of treatment,

28 parts by weight of the gas is used. The resulting solutionis thenheld at 38? C- After hours I precipitated in warm water. Sinee'ethylene'is .notvery appreciably soluble in water the cellulose acetate is precipitated in a finely divided fluffy form porous and. filledfwith fine bubbles. This productis less colored and less viscous than the check'product which was prepared without the additionof ethylene.

It is evident that various equivalents of the gases'herein given with many changes in the concentration thereof'or in the manner in which they'are introduced into the hydrolyzing bath maybe employed without departing from this invention or sacrificing any of its advantages.

. What we; claim as newand desire to besecured by Letters Patent of the United States is:

1; In the' process for thepreparationtof'an or ganic acid ester of cellulose the. step which com prises hydrolyzingithe cellulose esterin a bath containing'sulfur dioxide.

2. In the process for thepreparationof celluz-l lo'se acetate the step whichcomprises hydrolyzing the cellulose acetate. in a bath containing sulfur. dioxide. 1;: v

3.. In the process for the preparation of cellulose acetate the stepwhich comprises v addir'igj to the hydrolyzing bathan acetic acid solution .con.. taining sulfur dioxide. I, 4..I n-the process-for the preparation of. celluI- lose acetate the step whichcompriseshydrolyzing:

the celluloseacetate inan, acetic Iacidbathsatirf rated-with sulfur dioxide. v 5;.In the processfor thepreparationofran or}. ganicacid, ester of cellulose the step whichcome.

prises hydrolyzing the cellulose ester-rinaldeesterifying. bath containing a compound. having tetravalent sulfur and oxygen therein.

. 6. In. the process-for the preparation of ganic acidester of cellulose the step which:com;-

prises hydrolyzing the"cel-lulose ester in ade esterifying bath containing a compoundhaving a S02 radica1.

7. In the'process forthe preparationcfran or-g ganic acidester of cellulose the step which.com-- prises hydrolyzingthe cellulose ester in a bath: containing sulfurous acid.

'8. In the process for the preparationiofganic acidester of cellulose thestep which come. prises hydrolyzing the cellulose ester a. bath. oontaininga sulfite. 1.

9. In the process for the preparation. of or.-

ganic acid ester ofcellulosethe'step whichcom-.-

prises hydrolyzing the cellulose ester .in. as de esterifying bath in'which sulfur dioxide'gashas been dissolved.

CHARLES S. WEBBER; CYRILJ'. STAUD. r 

